Effects of physical and psychological multimorbidity on the risk of dementia: multinational prospective cohorts and a meta-analysis.

backgroundPrevious studies only considered the impact of a single physical or psychological disorder on dementia. Our study investigated the association of physical and psychological multimorbidity with dementia among older adults using two multinational prospective cohorts to supplement the limited joint evidence.

methodsWe utilized the Health and Retirement Study (HRS 2012 to 2018) in the United States (US) and the Survey of Health, Ageing and Retirement in Europe (SHARE 2012 to 2018). Physical disorder was defined as any one of seven self-reported physician-diagnosed conditions. Psychological disorder was assessed using the 8-item Center for Epidemiologic Research Depression (CES-D) scale or the EURO-D. Dementia was determined through a combination of self-reported physician diagnosis of dementia or Alzheimer's disease, or the 27-point HRS cognitive scale. Competing risk models were utilized to estimate the hazard ratios (HRs) and 95% confidence intervals (95% CI). DerSimonian-Laird random-effects meta-analyses were conducted to obtain pooled estimates.

resultsThe prevalence of physical and psychological multimorbidity was 17.29% (1027/5939) in continental Europe and 15.52% (1326/8543) in the US. The incidence of dementia was 6.21 per 1000 person-years in continental Europe and 8.27 per 1000 person-years in the US, respectively. It was highest among participants with physical and psychological multimorbidity in continental Europe (10.46 per 1000 person-years) and the US (14.82 per 1000 person-years), compared with the other three groups. In the univariate model, participants who reported physical and psychological multimorbidity had a higher risk of dementia compared with those who reported no physical and psychological disorders in continental Europe (HR = 2.59; 95% CI: 1.55, 4.33) and the US (HR = 4.11; 95% CI: 2.44, 6.94). After adjusting all covariates, the risk of dementia among participants who reported physical and psychological multimorbidity increased by 86% in continental Europe (aHR = 1.86; 95% CI: 1.08, 3.21) and by 176% in the US (aHR = 2.76; 95% CI: 1.61, 4.72), respectively. After pooling the outcomes, the risk of dementia among participants who reported physical and psychological multimorbidity increased by 115% (aHR = 2.15; 95% CI: 1.27, 3.03).

conclusionsPhysical and psychological multimorbidity was prevalent among older adults in the US and continental Europe. Given the consistent associations with dementia, it is imperative to increase awareness of the links and recognize the limitations of single-disorder care. Specific attention should be given to providing care coordination.